Question

A solution is prepared by dissolving 9.25 g of non-volatile solute in 450 mL of water. It has an osmotic pressure of 350 mm of Hg at 27°C. Assuming the solute is non-electrolyte, determine its molecular mass. (R = 0.0821 Lit-atm K⁻¹ mol⁻¹)

Answer 1

W_B = 9.25 g 

V = 450 mL = 0.450 L

π = `350/760` atm = 0.4605 atm

T = 273 + 27 = 300 K

R = 0.0821 Lit-atm K⁻¹ mol⁻¹

M_B = ?

`pi = n_B/V xx R xx T = W_B/(M_B/V) xx R xx T`

`350/760 = 9.25/(M_B/0.45) xx 0.0821 xx 300`

`9.25/(M_B) = 350/760 xx 0.45/(0.0821 xx 300)`

`(M_B) = (9.25 xx 760 xx 0.0821 xx 300)/(350 xx 0.45)`

M_B = 1099.35 g/mol⁻¹